Comparators are often employed in connection with devices such as data converters, control systems and feedback loops. Generally, detection circuitry is provided between a comparator and downstream circuitry. Hence, the comparator drives the inputs of the detection circuitry. Oftentimes, the circuitry which is downstream from the detection circuitry and receives the output of the detection circuitry is digital. For optimum performance, it is important for a detection circuit to be configured to quickly and consistently supply a single, definite output to the downstream circuitry. If the circuit fails to provide a stable output to downstream circuitry, data conversion speed and accuracy, for example, may suffer.
Normally, a comparator drives the inputs of a detection circuit to the supply rails, wherein the supply rails comprise the power supply to the detection circuit. Comparator metastability occurs when a comparator is not able to achieve a definite decision level for the downstream circuitry. Metastability may occur when the outputs of a comparator are balanced between the supply rails. A metastable condition may also occur if a differential between the outputs of the comparator (the inputs of the detection circuit) is too small. In such a case, the detection circuit may take too much time to attain a decision level. Another common metastable condition is when the comparator attains multiple decision levels within a single clock cycle, thereby confusing downstream circuitry.
The advantages of avoiding a metastability condition include, but are not limited to: improved data conversion speed and accuracy (i.e., lower Bit Error Rate (BER)), allowing new applications for older or generally unconventional circuit topologies, providing smaller comparator gain stages, providing less comparator gain stages, providing that control loops are more stable and providing that control loops have higher bandwidths.